In recent years, it has become accepted practice to groove the surface of highways and airport runways. The primary purpose of the grooves is to drain water from the surface to prevent aquaplaning of vehicles traveling over the surface.
If the surface is made of a rigid material, such as concrete, it is satisfactory to cut grooves in the surface which have a generally rectangular transverse cross section. However, it has been found that rectangular grooves are not as satisfactory for surfaces made of a relatively pliable or deformable material, such as asphaltic concrete, because the grooves tend to close under traffic. Once closed, the grooves are no longer effective for draining water from the surface. As a result, it has been common practice to specify grooves having a regular trapezoidal cross section; that is, a groove with a flat bottom wall and outwardly and upwardly diverging side walls. The cross sectional shape of the groove may also be described as an inverted truncated triangle.
The surface grooves are formed or cut with a grooving machine which drives gangs of abrasive cutting blades. The cutting blades generally include a circular metal core, or support disc, and a peripheral abrasive element which is normally made of a diamond abrasive material. The diamond abrasive material consists essentially of diamond particles distributed in a metal-base matrix and may comprise any of a number of standard and well known compositions.
Heretofore, the abrasive element for trapezoidal grooving consisted of a continuous rim, or edge around the periphery of the metal core. The abrasive element generally includes a transverse cross sectional configuration identical to the shape of the groove to be formed, that is, a generally regular trapezoidal shape with a rectangular base. In use, wear causes the configuration of the abrasive to change. Eventually, the configuration of the abrasive element approaches a rectangular shape. When this occurs the abrasive element is no longer capable of forming a groove having the desired configuration and the blade must be replaced. Since diamond abrasive blades are quite expensive, the wear life of the blades is an important consideration.